Various methods for detecting, locating and compensating digital errors have been published. Among such methods should be mentioned the use of error correcting and detecting codes. With this method control bits are added to the information bits for introducing error correction capability. Very powerful schemes can be obtained but the disadvantage with this method is that the transmitter must be modified to include the transmission of the control symbols. This disadvantage is eliminated by the present invention. The error smoothing apparatus is optional at the receiver. Thus it can be added to an already existing system without modifying the transmitter.
Furthermore, methods have been suggested which use the inherent redundancy in the bit stream both for identifying potential digital errors and for smoothing the effect of such errors. These schemes are also optional at the receiver without changing the transmitter but they are only using hard decision demodulation, thus not using the principle of unreliable bits identified by the soft decision demodulation. Such a receiver does not fully utilize all the potentially available information about error locations. Thus the error smoothing capability of such a device is suboptimal.